This invention relates to a channel division recording/reproducing apparatus adapted to divide a broad band signal such as a video signal into narrow band signals for a plurality of channels for recording and reproduction.
In order to record a video signal such as a television signal, etc., it is generally necessary that the frequency band of a recording system be made broad enough to meet that of the video signal. In an attempt to make the relative speed of a magnetic head and magnetic tape higher, for example, in a video tape recorder both the tape and the head may be rotated, but a structural difficulty is often encountered by doing so. Where, on the other hand, the magnetic head is not rotated, the travelling speed of the tape has to be made higher, presenting a structural problem. Moreover, more tape has to be used. Recently, attempts have been made to divide a video signal into narrow band signals for a plurality of channels and record them through a corresponding number of fixed heads. As such a division method, an Hadamard transformation is known which divides an original signal by sequency components similar to frequency components into a plurality of channel signals. The Hadamard transformation is one kind of an orthogonal transformation and an input signal is Hadamard-transformed using a Walsh function. Now suppose that a 2 MHz luminance signal is used as an input signal and that the Walsh function is a function of the eighth order. Then, the luminance signal is, after Hadamard transformation, divided into narrow band signals of eight channels of 250 KHz. The narrow band signals are frequency modulated for the respective channels and supplied to the magnetic heads. Now suppose that the carrier frequency of the respective modulators is set, for example, at 700 KHz, a value sufficiently higher than 250 KHz. Even if in this case a greater frequency deviation is taken, a modulation index can be made greater without involving a "beat" phenomenon between the luminance signal and the carrier signal, thus leading to an improvement in the signal-to-noise ratio (S/N ratio) as well as in the quality of a luminance signal recorded. In actual practice, however, the frequency of the carrier signal can not be sufficiently high in view of a relation between the travelling speed of the magnetic tape and the wavelength of the luminance signal. If the modulation index is made greater and a frequency deviation is made greater to improve the S/N ratio for a too low carrier frequency, a "beat" phenomenon occurs between the luminance signal and the carrier signal, thus degenerating the S/N ratio.